1. Field of the Invention
This invention relates to a prepreg article characterized by an extended shelf life of at least about three months at about 25.degree. C. for use in composites. More particularly, it relates to an essentially tack free prepreg article characterized by an extended shelf life of at least about three months at about 25.degree. C. for use in rigid, thermoset composite articles for structural, high impact and ballistic end uses. 2. Prior Art
Thermoset resin-containing solutions, or systems, for impregnating or coating reinforcing materials such as fibers for subsequent use in composites are known. These solutions typically comprise a resin, a catalyst for curing the resin, a solvent for adjusting the viscosity of the solution and a monomer for reacting with the polymer. The solvent and monomer are often the same entity, typically styrene.
A "prepreg" is at least one network of fibers, impregnated with just such a thermoset resin-containing solution, or system, but left uncured. Unfortunately, the prepregs impregnated with a styrene-containing system have a shelf life of only about two weeks and are very tacky to the touch at room temperature (about 25.degree. C.). The short shelf life is due to the fact that the styrene is unstable at room temperature and it evaporates from the thermosetting resin; once this develops, the prepreg can no longer be used as contemplated. The prior art addressed this problem by refrigerating or freezing the prepreg to extend its shelf life. However, the shelf life of a refrigerated or frozen prepreg is only about three months, and a refrigerated transport system for the prepregs is expensive.
The present invention was developed to overcome the deficiencies of the prior art.